The present invention relates to a fixing elastic member for supporting shadow mask of a color picture tube. Particularly, it relates to the elastic member with reduced permanent plastic deformation of elastic member caused by repetitive work of removal and attachment of the shadow mask from the color picture tube.
In the conventional color picture tube referring to FIG. 1, electron beams emitted from electron gun 5 of neck 3 and selected by shadow mask 6 are guided to radiate red, green and blue lights, emitting phosphor components of a luminescent screen formed inside of panel 1.
Only 20% of the electron beam is to pass through the shadow mask 6 and the remaining 80% will be absorbed by it. Due to this absorbed beam, the shadow mask 6 is expanded. This causes a change of distance between shadow mask 6 and panel 1, which results in the degrading of color purity. It is, however, to note that in this stage elastic member 8 is used to prevent the degrading of color purity resulted from the change of position. In other words, in a situation where a position change has occurred according to shadow mask's heat expansion by the electron beam emanated from electron gun 5, the elastic member 8 allows the shadow mask 6 to move from the position 9 to 9(a) toward the panel 1 in order to prevent degrading of color purity.
In the conventional elastic member design referring to FIG. 4, the welding point A of fixing portion 80 is located at 3/4 (three quarters) of fixing portion's length from top end 80a thereof where the plastic deformation of elastic member 8 occurs so often as the excessive force over the elasticity limit is applied to elastic member 8, due to the repetitive work of launching the shadow mask 6 to color picture tube. Moreover, the color purity is degraded when a member among several elastic members is deformed more than others, which causes the shadow mask deviation from a prearranged position.
As shown in FIGS. 2 through 4, the conventional elastic member comprises fixing portion 80 welded at the welding point A to mask frame 7 supporting shadow mask 6, a connecting portion 81 having a connecting hole 81a attached through panel pin 1a formed interior of the panel land a sliding portion 82 by which the fixing portion 80 and the connecting portion 81 form a one piece.
In this regard, the moving distance of shadow mask 6 moved toward panel 1 by elastic member 8 is the same as the length of sliding portion 82. Further it relates to the horizontal distance between fixing portion 80 and panel pin 1a.
Generally, in case of shadow mask using invar shadow mask with non-frame, the length of fixing portion is less than 5 mm, that of sliding portion is approximately 16 mm and that of connecting portion is around 18.5 mm, while the thickness of it is about 0.76 mm. With reference to FIG. 4, the welding point A of fixing portion 80 welded to mask frame 7 is located at three quarters of fixing portion's length from top end 80a thereof. And elastic member 8 has the limitation of transferring the shadow mask 6 to a certain distance toward panel 1. As a result, the length of sliding portion 82 has to be decided within a fixed range.
On the other hand, elastic member of second embodiment as shown in FIG. 5 comprises two pieces of the conventional elastic member shown in FIG. 4, welded symmetrically with each other so that it forms one elastic member.
Furthermore, the connecting portion 812 without any connecting hole is welded to mask frame 7 whereas the other connecting portion 81 with connecting hole 81a is attached through panel pin 1a. The sliding portion 811 connects the second fixing portion 813 and the connecting portion 812.
This type of elastic member, like one-piece elastic member, has a function of transferring shadow mask 6 toward panel 1 in order to prevent the degrading of color purity.
When the distance between the shadow mask and the panel changes due to heat expansion of the shadow mask; the problem of one-piece still applies to the two-piece elastic member because of the fact that the welding point A for fixing portion 80 and second fixing portion 813 is still located at three quarters of fixing portion's length from top end 80a thereof.